The present invention relates to a ship for the transport of liquid or gaseous cargo in tanks.
An example of such a ship is a tanker for the transport of liquid gases having a boiling point below ambient temperature at atmospheric pressure, typically a boiling point below -100.degree.C. Such a ship must be built as a double hull ship according to pending requirements; i.e., a ship with a double bottom and side tanks. Within the innermost ship's skin are the insulated cargo tanks and a second barrier--between cargo tanks and the innermost skin--to keep the liquid gas away from the innermost skin in case of leakage of a cargo tank, so that leaking gas cannot undercool the ship's hull and thus cause cold brittleness which might lead to fracture of the ship's hull. Furthermore, as additional security for said ships, transversely extending cofferdam partitions are prescribed as subdivisions between the insulated cargo tanks.
Such double hull ships are not entirely satisfactory for a number of reasons.
The enclosure of the cargo tanks, insulations, second barrier, side tanks and double bottom, etc. all require considerable ship space. And because the side tanks tend to be relatively narrow to conserve ship space, the cargo tanks, positioned immediately interiorly of the side tanks, are very vulnerable in case of collision.
Because it is at least difficult, and often impossible, to directly inspect the integrity of the tanks, the insulation and the second barrier, all spaces between the cargo tanks and the innermost ship's hull have to be neutralized with the aid of inert gas. In order to determine the existence of leakage from the cargo tanks, the inert gas must be continuously examined regarding the presence of traces of the cargo in the cargo hold.
The construction of the cargo tanks, the insulation and the second barrier (or leak pans) inside the ship's hull is both complicated and expensive to manufacture and maintain. For example, a special steel having a high cold-resistance characteristic must be utilized in the construction of those elements of the ship's hull abutting or enclosing the cargo tanks. Also irrespective of the pressure exerted by the cargo, difficulties often arise in connection with use of the various tanks, particularly in the integrity of welded seams and the second barrier.
The object of the invention is to provide a ship for the transport of liquid or gaseous cargo in tanks which is more efficient in its use of ship space, safer in the event of collision, easier to repair in the event of leaks, less complicated in structure, and more economical to build and operate.